The invention relates to a method of producing paper products made from a hygroreactive cellulosic fiber matrix sized with a hydrophobic material. The products produced are more dimensionally stable under cyclical humidity conditions than conventional paper products.
Conventional paper and paperboard products are made from hygrocellulosic fibers. These fibers tend to absorb moisture and swell in environments of high humidity and they tend to shrink in low humidity conditions. This dimensional instability in paper and paperboard products leads to problems such as curl, misregistering in printing, bulge, cockle, warp and compressive creep.
For example, a two sided polyethylene extruded release liner was found to exhibit wavy edges in cyclical humidity conditions. This in turn leads to product performance problems such as misregistration in a multicolor printing process.
These end use problems often result in costly project rejects. Thus, there is a need for dimensionally stable paper and paperboard products.
U.S. Pat. No. 3,753,069 to Crawford, U.S. Pat. No. 4,110,155 to Minogawa, U.S. Pat. No. 4,288,287 to Miyama, U.S. Pat. No. 4,331,508 to Miyoma, U.S. Pat. No. 5,178,936 to Kamiya, U.S. Pat. No. 5,194,362 to Nakabayashi, U.S. Pat. No. 5,254,450 to Lacy and U.S. Pat. No. 5,362,614 to Serizawa generally disclose resin coated photographic papers wherein resin stabilizers and/or antioxidants are incorporated into the paper core to help eliminate curl.
The prior art has shown use of sizing agents and paper saturants in the paper industry. Representative of these patents include U.S. Pat. Nos. 2,692,183, 2,629,648, 2,629,674 and 2,629,701 to Ericks; U.S. Pat. No. 4,133,688 to Sack, U.S. Pat. No. 4,152,190 to Serota, U.S. Pat. No. 4,522,686 to Dumas, U.S. Pat. No. 4,810,301 to Yoshioka, U.S. Pat. No. 4,849,131 to Sweeney, U.S. Pat. No. 4,935,097 to Tashiro, U.S. Pat. No. 5,160,484 to Nikoloff, and U.S. Pat. No. 5,374,335 to Lindgren.
Unlike the prior art, the present invention overcomes the problems typically associated with hygroreactive cellulosic fibers by providing paper and paperboard products that are more dimensionally stable under cyclical humidity conditions than conventional paper products.
Accordingly, it is a broad object of the invention to provide a dimensionally stable reprographic paper produced by sizing a cellulosic fiber matrix with a hydrophobic material. This technique reduces the hygroexpansion of the paper thus creating more dimensionally stable paper and paperboard products.
Another object of the invention is to reduce hygroexpansion of paper by approximately 40%, therefore creating more dimensionally stable paper and paper board. The technique involves a hydrophobic treatment of the paper which is then dried using heat and/or pressure.
A specific object of the invention is to provide a dimensionally stable release liner that is more stable against moisture changes and lays flat when subjected to cyclical humidity conditions. The base sheet of the release liner is surface sized with a hydrophobic material which permits adhesion of a polyethylene coating without the use of a primer or adhesion coating.
Another more specific object of the invention is to provide a dimensionally stable release liner having a balanced coating, i.e. using the same polyethylene on either side of the base sheet as well as the same coat weight on either side.
Another object of the invention is to provide a dimensionally stable paper or paperboard product with improved lay flat characteristics by surface sizing the base sheet to create a non-hygro reactive paper or paperboard.
In the present invention, these purposes, as well as others which will be apparent, are achieved generally by providing a process for producing dimensionally stable paper and paperboard by treating with hydrophobic materials to reduce the hygroexpansion of paper.
The process of the invention involves soaking the paper or paperboard in an aqueous solution of hydrophobes followed by drying using heat and/or pressure. Under pressure and/or heat the hydrophobe penetrates the paper fiber matrix making the fiber matrix hydrophobic, thus moisture is prevented from penetrating or exiting the fiber wall reducing fiber swelling and reswelling and the concomitant network expansion and contraction.
Various hydrophobic agents are used in the invention process. A preferred material is a modified cationic rosin emulsion. Other hydrophobic agents used in the invention process include ethylene oxide and propylene oxide block copolymer; polyethylene acrylate; alkyltrimethoxysilane; styrene acrylate copolymer dispersion; and polyurethane.
The aqueous solution of hydrophobic agents is preferably between 2 to 20 wt. % solids. In addition to the hydrophobic agent the aqueous solution comprises a hydrophilic sizing agent such as starch. The amount of starch used is typically between 8 to 12 wt. %. Other sizing materials used in preparing the invention include starch solutions such as ammonium persulfate converted pearl starch and Penford Gum 290. In a preferred embodiment the aqueous solution comprises approximately 1% hydrophobic agent, 10% starch and 89% water.
In general the invention provides a dimensionally stable reprographic paper and/or paperboard wherein the base sheet comprised of a hygroreactive cellulosic fiber matrix is sized with a hydrophobic agent. The resulting treated paper or paperboard is hydrophobic and has a contact angle of 90xc2x0 or greater.
In accordance with a specific embodiment of the invention, a two-sided polyethylene extruded release liner is produced. The base sheet is prepared in accordance with the invention process. Preferably the base sheet is treated with a hydrophobic solution, preferably a modified cationic resin (commercially available as Sizeall XR 4177 from Ariziona Chemical, Panama City, Fla.) and then coated with two sheets of polyethylene on opposite sides of the base sheet to form the release liner.
Other objects, features and advantages of the present invention will be apparent when the detailed description of the preferred embodiments of the invention are considered with reference to the drawings, which should be construed in an illustrative and not limiting sense as follows: